Method of manufacturing articles from particulate metal masses



United States Patent US. Cl. 75--214 5 Claims ABSTRACT OF THE DISCLOSURE Producing articles from particulate metal, by pressing the metal in a die to shape the article, with die surfaces and the metal mass where contacting such surfaces maintained substantially below subzero temperatures, and after shaping sintering the articles to coalesce the articles therein into an integrated solid mass.

This invention relates to the production of articles from aluminum, its alloys, and like metals which when shaped according to conventional procedures tend to gall, to smear and to produce locking of die parts used in shaping the article.

Powder metallurigical techniques have been proposed for manufacturing a wide variety of articles, Which have demonstrated certain advantages over other known forms of fabrication. Conventional powder metallurigical techniques have comprised pressing a mass of metal in a die thus to shape the article, and then sintering the consolidated product produced. While such procedures are beneficially used with a number of metals, certain difficulties are encountered when producing articles from metals such as aluminum, aluminum alloys, beryllium and like metals. Further explaining, when a mass of aluminum particles is compressed in a die, the aluminum tends to adhere to the die surfaces contacting the aluminum, causing galling and smearing upon removal of the article from the die with imperfectly shaped articles resulting. Further, adhesion between the aluminum and die parts tends to cause locking together of the die parts, whereby substantial pressures are needed to produce release. Excessive Wear of the die parts is a direct result of such locking together of the die parts.

Attempts have been made to take care of such adhesion problems by using in the die paraffin or other lubricants. However, known lubricants have not been entirely successful in eliminating the galling, smearing and locking tendencies noted. Further, the use of a lubricant tends to complicate the manufacture of the parts.

Generally, an object of this invention is to provide an improved method for manufacturing parts from particulate metal masses, wherein the problems noted above attributable to adhesion are reduced substantially, if not eliminated.

More specifically, an object of the invention is to provide a novel method of manufacturing articles from aluminum, alloys of aluminum and related metals, which enables articles to be pressed in dies with substantial reduction of smearing, galling and locking problems.

According to the invention, and describing a preferred embodiment, the die parts, and the particulate metal mass which is to be consolidated into an "article, are cooled to a temperature substantially below 0 C, More specifically, temperatures of 40 C. are employed, and preferably tempreatures below about -60 C. With such temperature conditions substantially maintained during pressing in the die, an article may be produced which is easily removed from the die, and which when removed reflects substantially all the detail of the shaping surfaces in the die parts. On such an article being raised to room temice perature, some thermal expansion of the article takes place. After sintering, to coalesce the particles in the mass of the article, it has been noted that the dimensions of the article remain substantially the same as before sintering. This is particularly true if compacting pressures exceeding about 11 tons per square inch are used in the die. Repeated pressings are possible, with substantially no die wear observed.

The particular reasons for the novel results obtained are not entirely understood. Thus, while some cooling of rolls has sometimes been used in sheet rooling processes, nothing in such processes suggests that with such a subtantial reduction in temperatures, the adhesion problems encountered when processing aluminum and like materials may be controlled. The beneficial results of the invention cannot be entirely explained by the decrease in ductility of the metal which occurs with such low temperatures, as certain metals having substantially the ductility of aluminum and its alloys have been converted into articles using powder metallurgical techniques of pressing and sintering, without the galling and related problems noted when aluminum is so processed.

Various other novel features and objects of the invenion will become more fully apparent as the following description is read in conjunction with certain specific examples, included for the purpose of illustration only.

Ordinarily and following the process of the invention, it is contemplated that powders of the processed metal be employed, since such have been found to produce good reproduction in the pressed article of the die surfaces forming the article. However, needles, flakes and pellets have been compacted by the process with good results obtained, The invention, therefore is disclosed in connection with the production of articles from a particulate metal mass, which term is intended to cover all such forms of metal product.

While it is believed that the benefits of the invention result when the die surfaces and the portions of the metal mass actually contacting such surfaces are maintained during the pressing operation at the temperature level set forth, as a practical matter and to minimize the effects of ambient heat, it is contemplated that the bodies of the die parts and that the entire metal mass being processed both be reduced to proper subzero temperature before the pressing operation. With the die bodies of the parts and metal mass so cooled, the parts may be assembled in a press and the metal mass poured into the die with little significant rise in temperature in the parts and metal mass, even though room temperature conditions exist around the press employed to produce consolidation of the metal. with the environment about the die parts when located in the press controlled, whereby subzero temperatures may be maintained in such environment, the effects of ambient heat may be reduced or substantially eliminated.

The following example illustrates the manufacture of cylindrically shaped parts according to the invention:

EXAMPLE I An Airdie ISO-s female compacting die, having an inner diameter of 1.5175", and an Airdie ISO-s male punch and plug, having outer diameters of 1.5170", were employed as the die parts. The parts, which were made of steel, were immersed in a bath of acetone cooled with cakes of Dry Ice. Aluminum powder mesh) was placed in a glass beaker and immersed in the bath together with the die parts. After the powder and die parts both had reached bath temperature (about -50 C.), the die parts were removed and assembled as quickly as possible in a 100 ton press. About 25 grams of the aluminum powder was then poured into the die, and the powder compressed using a force in the press of 30 tons (a pressure of about 17.0 tons per square inch). A com- 3 pact was produced of cylindrical shape, having a diameter of about 1.5" and a height of about 0.4".

The resulting compact was easily removed from the die components. Visual inspection of the compact revealed no smearing or galling. No metal particles were evident adhering to the die components and substantially no die wear was noted in the components. Subsequent compacts produced using the same procedure were removed as easily from the press, and were equally as good in appearance.

Compacts Were also produced using the aluminum powder and die parts indicated, with the die parts and aluminum at room temperature. The powder adhered to the die components badly, and some 45 tons of force were required to remove the compact and male die parts. Alu minum had to be removed from the female die and top male punch by grinding. All steel components were scoured in this experiment.

The following example illustrates the production of an article from aluminum and boron carbide.

EXAMPLE II A mixture was prepared of 65 parts l= mesh aluminum powder, and 35 parts 100 mesh boron carbied (B C) powder. Airdie male and female die parts, together with the metal mixture, were cooled as in the first example, in acetone and dry ice, until they reached bath temperature of approximately 65 C. The die parts were assembled in a 100 ton press, and approximately 25 grams of the metal mixture poured into the die to prepare a compact. The mixture was then compressed by actuation of the ram in the press. Using such a procedure five different compacts were prepared.

Dimensions of the compacts were taken after compaction and while cold, and after overnight room temperature warm-up. The compacts were sintered for four hours after such room temperature warm-up, at 600 C, in a vacuum. Dimensions of the compacts were taken again after sintering.

The following table summarizes the results obtained in the manufacture of such compacts. As the table indicates, in the manufacture of the different compacts, the ram force used in the press was varied from to 30 tons, with a pressure variation on the compacts resulting of from about 5.7 to 17 tons per square inch. As the table further demonstrates, with a pressure used greater than about 11 tons per square inch, the dimensions of a compact before and after sintering remain approximately the same.

Compact Compact Ram Pressure, Compact O.D., in. O.D., in. force, tons per 0.D., in. Rm. after tons sq. in. 65 C. Temp. siut.

Visual inspection of the die parts used in preparing the compacts showed substantially no discernible wear after their preparation. All of the compacts were removed easily from the die parts with no galling or smearing evidenced.

Pressing of compacts using temperatures of about 0 C. do not result in the marked improvement in the inhibition of galling, smearing and locking of die parts noted when the much lower temperatures of the invention were employed. With temperatures utilized in the range of 40 C., some improvement in handling ease and workability was noted, but optimum results apparently are obtained with lower temperatures ranging downwardly from about -60 C.

The invention, of course, has particular utility in connection with the manufacture of complex shapes. For instance, screw parts, fittings and other articles of complex configuration are produceable according to the invention where such parts are difficult, if not impossible to manufacture, using conventional powder metallurgical techniques.

While various embodiments of the invention have been described, obviously variations and modifications are possible without departing from the invention. It is desired to cover all such modifications of the invention as would be apparent to one skilled in the art, and that come within the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. A method of manufacturing articles from metal which exhibits galling and smearing tendencies when pressed such as aluminum, beryllium and their alloys, comprising pressing particulate metal in a die to shape the article and maintaining the surfaces of the die which contact the metal mass, and the metal mass where such contacts die surfaces, at an operating temperature which is below about -40 C. and preferably below 60 C.

2. The method of claim 1, wherein the particulate mass of metal is cooled to said operating temperature prior to being introduced to said die.

3. The method of claim 2, wherein the bodies of the die parts are cooled to said operating temperature prior to the mass of the metal being introduced to the die.

4. The method of claim 1, wherein the articles after pressing are removed from the die, and subsequently sintered.

5. The method of claim 1, wherein the particulate mass of metal is cooled to said operating temperature prior to being introduced to the die, the bodies of the die parts are cooled to the operating temperature prior to the mass of the metal being introduced to the die, and wherein the article after pressing is removed from the die and subsequently sintered.

References Cited UNITED STATES PATENTS 3,356,495 12/1967 Zima 2l4 3,366,479 1/1968 Storchheim 752l4 FOREIGN PATENTS 1,015,197 12/1965 Great Britain.

CARL D. QUARFORTH, Primary Examiner A. I. STEINER, Assistant Examiner US. Cl. X.R. 75200; 264-111 

